We have an urgent message about some critical new scientific research. It strongly suggests that requiring fabric mask use in public places could be amongst the most powerful tools to stop the community spread of COVID-19.

People are most infectious in the initial period of infection, when it is common to have few or no symptoms

Cloth masks obstruct a high portion of the droplets from the mouth and nose that spread the virus

Non-medical masks have been effective in reducing transmission of coronavirus

Cloth masks can be washed in soapy water and re-used

Places and time periods where mask usage is required or widespread have been shown to substantially lower community transmission

Public mask wearing is most effective at stopping spread of the virus when the vast majority of the public uses masks

Laws appear to be highly effective at increasing compliance and slowing or stopping the spread of COVID-19.

The preponderance of evidence, in both laboratory and clinical settings, indicates that mask wearing reduces the transmissibility per contact by reducing transmission of infected droplets. The decreased transmissibility could substantially reduce the death toll, other harms to public health, job losses and economic losses. The cost of such masks is very low by comparison.

Modeling suggests that widespread public mask use, in conjunction with other measures, could bring the effective reproduction number (R) beneath 1.0, thus halting the growth of the pandemic.

Therefore, we ask that government officials require cloth masks to be worn in all public places, such as stores, transportation systems, and public buildings as soon as possible. This action will prevent people who are infectious from unknowingly spreading the disease.

We also ask business leaders who offer products and services to the public to require their employees and customers to wear masks whether or not it is required by local law. This vital step will help protect workers and customers.

Such requirements will greatly increase the rate of mask wearing. This should be done in conjunction with, not as a replacement for, hand hygiene, physical distancing, testing, and contact tracing strategies.

This requirement should be introduced alongside clear guidelines for the production, use and sanitization or re-use of face masks. We urge you to also consider their distribution as shortages allow.

There is no need to wait for availability of medical-grade masks; any face covering, including a piece of cloth, a scarf, bandana, t-shirt, or paper towel, appears to be effective.

Sincerely,

Organizing Signatories

Note: institutional affiliation is provided for identification purposes only and does not indicate or imply an endorsement of the views expressed in this letter by any institution.

Jeremy Howard: Distinguished research scientist, University of San Francisco, co-founder fast.ai, member World Economic Forum Global AI Council